A Membrane Contactor Enabling Energy-Efficient CO₂ Capture from Point Sources with Deep Eutectic Solvents

We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO₂ capture. This process uses a deep eutectic solvent (DES) in an HFMC to provide close interfacial interactions and contact between the DES and CO₂. This approach overcomes disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO₂ capture methods. Commercial low-cost polymer hollow fiber membranes (e.g., microporous polypropylene) were evaluated for CO₂ capture with reline, a prototypical DES. Single-gas measurements showed that the DES-based polypropylene HFMC can capture and separate CO₂ while rejecting N₂. From a mixed gas containing 50 mol % N₂ and 50 mol % CO₂, the DES-based HFMC separated CO₂ with a purity of 96.9 mol %. The effect of several process parameters including solvent flow rate, pressure, and temperature on the CO₂ separation performance was studied. The flux of the recovered CO₂ was 67.43 mmole/m²/h at a feed pressure of 4 bar. In situ Fourier transform infrared (FTIR) measurements combined with density functional theory (DFT)-based molecular dynamics simulations revealed that reline absorbs CO₂ by physical absorption without forming a new chemical compound, and CO₂ separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about physical solvent-based separation processes and a pathway toward practical deployment.